This research project will address the process of bone remodelling, specifically the role of cytokines in the development and functioning of osteoclasts. In Aim 1, the cytokine gene regulation of activated macrophages will be studied in culture systems stimulated with lipopolysaccharide (LPS). The representative osteolytic cytokines tumor necrosis factor (TNF), macrophage inflammatory protein (MIP), and interleukin 6 (IL-6) will be studied to measure gene expression and activation of the transcriptional regulatory protein NF kappa B. The bioactivity of TNF and IL-6 produced by stimulated macrophages will be calculated. The data from the above studies will provide a foundation for the long- term bone marrow culture experiments in Aim 2. These studies will examine the communication network between hematopoietic/osteoclast progenitors and their supporting stromal/osteoblast cells during osteoclast maturation and function. Aim 2(a) will establish the optimal culture conditions for osteoclast-like cell enrichment, as well as methods to assay osteoclast- like cell number and function using tartrate resistant acid phosphatase staining and scanning electron microscopy. Aim 2(b) addresses the effect of LPS on osteoclast development in primary bone marrow cultures utilizing the LPS non-responsive murine strain C3H/Hej and the (LPS responsive) control C3H/Fej strain. Aim 2(c) examines the role of factors produced by LPS induced stromal/osteoblast cells on osteoclast development and function utilizing the C3H/Fej and C3H/Hej murine strains. These studies will take advantage of the well characterized stromal cell line derived from control (BMS2) and osteopetrotic (OP) mice.